Central Coast residents were mesmerised by a unique cloud formation which was clearly visible on the afternoon of June 4.
The unique weather phenomenon stretched for around 300km over the skies of the NSW coast for around three hours.
Theories ranged from extraterrestrial influences to a chemical event.
But in fact, they were roll clouds – long tube-like clouds which are rare across most of the world.
These roll clouds were produced by atmospheric gravity waves that formed over eastern NSW on Tuesday morning.
The invisible waves in the atmosphere caused elongated areas of rising air that cooled enough to produce parallel bands of cloud.
Bureau of Meteorology senior meteorologist Christie Johnson said the formation was a rare phenomenon, requiring a specific mix of ingredients.